1. Field of the Invention
The present invention relates to a method and apparatus for applying tension to a string of coiled tubing during its injection into and withdrawal from a well bore. More particularly, the invention relates to a device used with a wheel-type tensioner, which contact and supports the tubing over an arc length of less than 180°.
2. Description of the Related Art
Currently wheel-type tensioners are commonly used with coiled tubing employed in servicing petroleum wells. For such devices, the tubing is stored on a large reel and is then passed over a tensioning wheel before entering the wellbore. The tubing only contacts the wheel of the tensioner over an arc length of less than 180° and typically less than 90°.
The wheel provides a turning function for the tubing so that it can be routed between the well bore and the storage reel, but the wheel can also provide tensioning capability if motive torque is applied. However, when the tubing must be forced into the well through a sealing gland and against well pressure or when the tubing must be withdrawn from the well, the ability of the wheel to apply motive tension to the tubing is limited.
The tension which can be applied by the simple wheel tensioner is controlled by the length of arc contact, the tubing tensions entering and leaving contact with the wheel, and the coefficient of friction of the tubing with the wheel. These limitations are particularly important when only a short length and weight of tubing are in the well.
A need exists for a means of enhancing the radial contact forces and resultant frictional forces between the tubing and the wheel of the tensioner. A further need exists for a simplified and cost-effective means for enhancing the radial contact forces and resultant frictional forces between the tubing and the wheel of the tensioner.